In mechanised forestry, use is made of feeding devices of the type described above, both in one-grapple harvesters (processing standing trees by felling, limbing and cutting) and in twin-grapple harvesters or processors limbing and cutting trees already felled. In one-grapple harvesters, the feeding units generally consist of so-called spiked rollers, while vehicle-type rubber wheels are generally employed in twin-grapple harvesters. In recent times, attempts have also been made to use different types of endless rotary belts for this purpose. Especially promising is the type of feeding units disclosed in SE patent application 8601628-4, utilising a plurality of links provided on the outside of a rigid guide bar and together forming an endless belt-like element.
A general desire in forest machinery is to reduce the dimensions and the weight of the components used, including the feeding units. However, this desire gives rise to problems in such cases where the harvester should be uesd for both large and small trees since the feeding units must then be designed with an exceptionally large width to be able to process trees within the entire dimensional range which in practice goes from about 40 mm (small trees from thinnings) up to 400-500 mm (full-grown trees from final fellings).